Conventionally, a torque wrench with a torque limiter that uses a cam mechanism is known, which has a configuration in which a cylindrical head portion is attached to a distal end of a cylindrically formed lever. In the head portion, transmission shaft with a square shaft portion, to which an engaging portion such as a hexagonal socket or the like to engage with a fastener such as a bolt or nut is removably attached, is mounted via a ratchet mechanism such that the shaft can rotate only in one direction. When a tightening force is manually applied to the lever and the tightening torque reaches a specified torque, the torque limiter disposed between the head portion and a distal end portion of the lever is activated, so that the fastener is released from the tightening force transmitted thereto (Patent Literature 1).
In the configuration of this torque limiter using a cam mechanism, a cylindrical cam shaft having a plurality of cam parts continuously formed in the circumferential direction on the outer circumferential surface thereof is rotatably disposed inside a cylindrically formed head body, while a cam follower in the form of a columnar roller is pressed against the cam part via a thrust pad mounted to a distal end portion of a torque adjusting spring disposed inside the cylindrical lever. The roller can move in the axial direction of the lever to abut on an inner circumferential surface of the lever. A plurality of ratchet teeth are formed in the circumferential direction on the inner circumferential surface of a shaft hole in the cam shaft, while a main shaft portion of the transmission shaft is rotatably disposed in the shaft hole, so that ratchet claws attached on the outer circumference of the main shaft portion engage with the ratchet teeth. A rotation imparted to the cam shaft in a tightening direction causes the ratchet claws to engage with the ratchet teeth to rotate the transmission shaft, whereby the fastener such as a bolt is tightened.
The cam part of the cam shaft forming the torque limiter is configured such that a torque transmitting cam surface which is a steep slope and a torque non-transmitting cam surface which is a gentle slope are formed on both sides of a cam top. The roller waits in a state where it is pressed against a torque transmitting cam surface of the cam part. A tightening force transmitted via the lever to the roller causes the camshaft to rotate in the tightening direction via the torque transmitting cam surface. As the tightening force to the fastener such as a bolt increases, the reaction force from the torque transmitting cam surface to the roller increases, whereby the roller moves toward the cam top against the spring force of the torque adjusting spring. When the roller goes over the cam top, the roller stops applying the force that rotates the camshaft in the tightening direction, whereby the user is notified that the specified torque has been reached.